Interferons are proteins which are secreted by eukaryotic cells after virus infections or other stimulations and may in turn protect the cells from virus infections. Three classes of interferons are known at present: they are referred to as interferon-.alpha., interferon-.beta. and interferon-.gamma. (abbreviated to IFN-.alpha., IFN-.beta. and IFN-.gamma.). They differ in their structure and effects. Thus, interferons may have a regulating effect on the cells of the immune system or they may also influence the differentiation of cells and the growth of tumours.
In 1965 F. Wheelock discovered a polypeptide which protected certain cells from virus infections (Science 149, 310 (1965). Polypeptides with these properties are referred to as immune interferon, type II interferon, interferon-gamma or IFN-.gamma., although they are polypeptides belonging to the class of the lymphokines. In addition to human interferon-.gamma., bovine, murine and rat interferon-.gamma. have also become known. All the .gamma.-interferons known hitherto occur in glycosylated form, although the glycosylation has no influence on the biological activity (Keller et al., J. Biol. Chem. 258, 8010 (1983)).
For a long time, it had been assumed that interferons had a species-specific activity. In vitro tests, however, showed that IFN preparations from cattle could trigger an antiviral activity in monkeys and humans (Tovey, M. G. et al. J. Gen. Virol. 36, 341-344 (1977). This species interactivity might possibly be connected with the more or less great homology of the genes or proteins: it has not been possible to test this assumption owing to the small amounts of animal interferons.
In spite of the species interactivities detected, side-effects such as antigenicity are observed when interferons from different species are used and these are unacceptable in therapy.
Since, however, animal husbandry and the keeping of domestic pets have considerable economic importance, there is a need for interferons for various species which can be used by veterinary surgeons.
Highly purified animal interferon of various species would moreover offer the welcome opportunity of investigating the mechanisms of activity for interferons in order to arrive at models which could be transferred to man.
The first investigations with animal interferons were carried out using preparations from natural cell material; the yield and purity of the interferons prepared by this method make them unsuitable for the preparation of drugs.
By developing the recombinant DNA technique it is possible to produce heterologous proteins from microorganisms. In this way, for example, human interferons (Hu-IFN) have been prepared and most recently various non-human inter ferons have also been obtained.